1. Field of the Invention
The present invention relates to an apparatus for processing character or image information, and more particularly to an apparatus which reads or reproduces information by deflecting a light beam, e.g., a laser beam emitted from a laser beam source. The present invention also relates to an optical unit incorporated in the information reading/reproducing apparatus.
2. Description of the Related Art
An image reader is well known as an example of an information-entering apparatus connectable to a computer. The image reader irradiates a given object with a light beam emitted from a light source, and reads information from the light beam reflected by the object. The light beam emitted from the light source is deflected by an optical deflector, such that it is linearly incident on a desirable position on the object. The optical deflector is capable of changing the beam-deflecting angle steplessly, thus allowing the deflected beam to travel in a desirable direction.
The light source and optical unit mentioned above are integrally assembled as part of an optical unit.
The above optical unit can be employed in an image-forming apparatus of a type which visualizes the information supplied from a host computer and forms a hard copy on a sheet; it can be employed in a digital PPC copying machine, for example.
In addition to the above-noted light source and optical deflector, the optical unit comprises the following: a collimator lens, a focusing lens and a horizontal synchronization detector. The light source is normally constituted by a semiconductor laser diode and incorporates a monitor diode for monitoring the intensity of laser beam emitted from the laser diode. The collimator lens collimates the laser beam to provide it with desirable characteristics, and the optical deflector deflects the collimated laser beam. The focusing lens focuses the deflected laser beam such that the laser beam is focused at a desirable position on a given object. The horizontal synchronization detector matches the horizontal synchronization of the laser beam deflected in the main scanning direction of the object. In general, the horizontal synchronization detector is a photodetector. This photodetector is located outside of a region where the laser beam directed to the object traces an image. The photodetector detects whether the position of the deflected laser beam coincides with the deflection start position determined in the sub scanning direction of the object.
The laser beam emitted from the laser diode is made to have a desirable sectional shape by the collimator lens, and is then deflected by the optical deflector such that it is directed toward the object. The laser beam is focused on the desirable position on the object by the focusing lens.
Each time the laser beam is deflected by the optical deflector, part of the laser beam is cyclically incident on the photodetector which is arranged at the above-noted position is the optical path located between the optical deflector and the object. The laser beam incident on the photodetector is detected as a horizontal synchronization signal.
The horizontal synchronization signal is fed back to the circuit which energizes the laser diode. The signal, thus fed back, is used for controlling the deflection start position of a laser beam already deflected in the main scanning direction of the object such that it corresponds to the deflection start position of a laser beam to be deflected next.
The optical unit is undesirably large in size since it has to contain the following: a photodetector used for detecting a deflected laser beam; a group of electric circuits including a control circuit for converting a signal detected by the photodetector into an electric signal and a transfer circuit for transferring the signal from the control circuit to a main controller; wiring members for connecting the detector and the electric circuits in a predetermined manner; etc. In addition, the electric circuits used for the horizontal synchronization detector are arranged in the optical unit such that they are independent of the electric components of the apparatus which incorporates the optical unit. This being so, measures should be taken for preventing noise between the optical unit and the apparatus. Therefore, the number of parts employed in the apparatus is large, and cost for manufacturing the apparatus is inevitably high.